U.S. patent number 5,317,551 [Application Number 07/729,140] was granted by the patent office on 1994-05-31 for optical disk head including a light path having a thickness and width greater than the light beam wavelength by a predetermined amount.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Teruhiro Shiono.
United States Patent |
5,317,551 |
Shiono |
May 31, 1994 |
**Please see images for:
( Certificate of Correction ) ** |
Optical disk head including a light path having a thickness and
width greater than the light beam wavelength by a predetermined
amount
Abstract
An optical disk head which includes a substrate, a light path
for allowing light beam to propagate in a zigzag form, having a
thickness and width of 10 times greater than the wavelength, a
light source optically connected to the light path so as to allow
an incident light from the light source to propagate therethrough,
a first light condenser optically connected to the light path so as
to radiate the light beam propagated through the light path upon an
object provided toward a top surface of the substrate, a second
light condenser for guiding the light beam reflected from the
object into the light path, and an optical detector for detecting
the light beam propagated through the light path guided by the
second light condenser.
Inventors: |
Shiono; Teruhiro (Osaka,
JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
|
Family
ID: |
26505278 |
Appl.
No.: |
07/729,140 |
Filed: |
July 12, 1991 |
Foreign Application Priority Data
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Jul 16, 1990 [JP] |
|
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2-189052 |
Jul 16, 1990 [JP] |
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2-189053 |
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Current U.S.
Class: |
369/44.12;
359/571; 369/103; 369/112.07; 369/112.09; 369/112.12; 369/112.14;
369/44.23; G9B/7.109; G9B/7.113 |
Current CPC
Class: |
G02B
5/1876 (20130101); G02B 5/1885 (20130101); G02B
6/1245 (20130101); G11B 7/124 (20130101); G02B
6/43 (20130101); G11B 7/1353 (20130101); G02B
6/34 (20130101) |
Current International
Class: |
G02B
6/43 (20060101); G02B 6/124 (20060101); G02B
5/18 (20060101); G02B 6/34 (20060101); G11B
7/12 (20060101); G11B 7/135 (20060101); G11B
007/00 () |
Field of
Search: |
;369/44.11,112,109,103,110,111,124,44.12,44.23,100,44.24,122
;359/742,571-575 ;385/14,129,130,131 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0226647 |
|
Jan 1987 |
|
EP |
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0394865 |
|
Oct 1990 |
|
EP |
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3921406 |
|
Apr 1990 |
|
DE |
|
62-146443 |
|
Jun 1987 |
|
JP |
|
110433 |
|
Jan 1989 |
|
JP |
|
2-301702 |
|
Dec 1990 |
|
JP |
|
2-301703 |
|
Dec 1990 |
|
JP |
|
2-301704 |
|
Dec 1990 |
|
JP |
|
Other References
Book, "Autofocus Hitec Technologies", edited by M. Kohno (with
English translation), pp. 291-298 (undated). .
"Planar Integration of Free-Space Optical Components" by Jurgen
Jahns and Alan Huang, Applied Optics, vol. 28, No. 9, May 1,
1989..
|
Primary Examiner: Psitos; Aristotelis
Assistant Examiner: Hindi; Nabil
Attorney, Agent or Firm: Panitch Schwarze Jacobs &
Nadel
Claims
What is claimed is:
1. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a first light condensing means optically connected to
the light path so as to radiate the light beam propagated through
the light path upon an optical recording medium provided over a top
surface of the substrate, a second light condensing means for
guiding the light beam reflected from the optical recording medium
into the light path, and an optical detector for detecting the
light beam propagated through the light path guided by the second
light condensing means, the first light condensing means being a
diffractive optical component having a curved grating which
comprises a plurality of curves which are bulged in the direction
in which the light beam from the light source are propagated and
symmetrical with respect to the center line of the propagating
light beam.
2. An optical disk head according to claim 1, wherein the thickness
and width of the light path is not smaller than 100 times the
wavelength of the light beam propagated through the light path.
3. An optical disk head according to claim 1, further comprising a
position detecting optical means.
4. An optical disk head according to claim 1, wherein the light
path is disposed within the substrate.
5. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a first light condensing means optically connected to
the light path so as to radiate the light beam propagated through
the light path upon an optical recording medium provided over a top
surface of the substrate, a second light condensing means for
guiding the light beam reflected from the optical recording medium
into the light path, and an optical detector for detecting the
light beam propagated through the light path guided by the second
light condensing means, the second light condensing means being a
diffractive optical component having a grating which comprises a
plurality of curves which are bulged in the opposite direction to
the direction in which the light beam introduced into the light
path by the second light condensing means are propagated and
symmetrical with respect to the center line of the propagating
light beam.
6. An optical disk head according to claim 3, wherein the position
detecting optical means is an optical beam splitter.
7. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a first light condensing means optically connected to
the light path so as to radiate the light beam propagated through
the light path upon an optical recording medium provided over a top
surface of the substrate, a second light condensing means for
guiding the light beam reflected from the optical recording medium
into the light path, an optical detector for detecting the light
beam propagated through the light path guided by the second light
condensing means, and a position detecting optical means comprising
an optical beam splitter, the optical beam splitter being a reflex
diffractive optical component disposed on the top surface of the
substrate so as to face the optical recording medium, and including
a pair of lenses, the pattern of each grating comprising a group of
ellipses having equal eccentric ratios and major axes in the
direction in which the light beam is propagated, wherein the
centers of the ellipses are shifted one after another progressively
in the opposite direction to the direction in which the light beam
is propagated and the grating period diminishing toward the outside
peripheries.
8. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a first light condensing means optically connected to
the light path so as to radiate the light beam propagated through
the light path upon an optical recording medium provided over a top
surface of the substrate, a second light condensing means for
guiding the light beam reflected from the optical recording medium
into the light path, an optical detector for detecting the light
beam propagated through the light path guided by the second light
condensing means, and a position detecting optical means comprising
an optical beam splitter, the optical beam splitter comprising a
pair of reflex micro-Fresnel lenses disposed on the top surface of
the substrate.
9. An optical disk head according to claim 1, wherein the light
path comprises a collimator for collimating the light beam
propagated through the light path from the light source.
10. An optical disk head according to claim 9, wherein the
collimator is a reflex diffractive optical component.
11. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a first light condensing means optically connected to
the light path so as to radiate the light beam propagated through
the light path upon an optical recording medium provided over a top
surface of the substrate, a second light condensing means for
guiding the light beam reflected from the optical recording medium
into the light path, and an optical detector for detecting the
light beam propagated through the light path guided by the second
light condensing means, the light path comprises a collimator for
collimating the light beam propagated through the light path from
the light source, the collimator being a reflex diffractive optical
component, the collimator comprising gratings which include a
plurality of ellipses having major axes in the direction in which
the light beam is propagated, wherein the centers of the curves are
shifted one after another progressively in the direction in which
the light beam is propagated.
12. An optical disk head according to claim 9, wherein the
collimator in a micro-Fresnel lens.
13. An optical disk head according to claim 10, wherein the first
and second light condensing means are transmission off-axis lenses
disposed on the top surface of the substrate so as to face on the
optical recording medium, and wherein the beam splitter and the
collimator are disposed on the top surface of the substrate.
14. An optical disk head according to claim 1, wherein the light
source and the optical detector are disposed on the top surface of
the substrate so as to face the optical recording medium.
15. An optical disk head according to claim 13, wherein the light
source and the optical detector are disposed on the bottom surface
of the substrate.
16. An optical disk head according to claim 15, wherein the light
source and the collimator are disposed in correspondence to each
other with the substrate being interposed, and wherein the optical
detector and the optical beam splitter are disposed in
correspondence to each other with the substrate being
interposed.
17. An optical disk head according to claim 1, wherein the first
and second light condensing means are reflex off-axis lenses, and
disposed on the bottom surface of the substrate.
18. An optical disk head according to claim 1, wherein the second
light condensing means is a transmission diffractive beam splitter,
and disposed on the top surface of the substrate, and the split
light beam is detected by the optical detector.
19. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a first light condensing means optically connected to
the light path so as to radiate the light beam propagated through
the light path upon an optical recording medium provided over a top
surface of the substrate, a second light condensing means for
guiding the light beam reflected from the optical recording medium
into the light path, and an optical detector for detecting the
light beam propagated through the light path guided by the second
light condensing means, the second light condensing means being a
transmission diffractive beam splitter disposed on the top surface
of the substrate, the split light beam being detected by the
optical detector, the second light condensing means comprising a
pair of gratings which includes a plurality of curves bulged in the
opposite direction to the direction in which the light beam
introduced by the second light condensing means into the light path
are propagated therethrough, the curved being symmetrical with
respect to the center line of the propagating light beam.
20. An optical disk head according to claim 19, wherein the light
source and the optical detector are disposed on the top surface of
the substrate.
21. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a light condensing means optically connected to the
light path so as to radiate the light beam propagated through the
light path upon an optical recording medium provided over a top
surface of the substrate and for guiding the light beam reflected
from the optical recording medium into the light path, and an
optical detector for detecting the light beam propagated through
the light path guided by the light condensing means, the light
condensing means being a diffractive optical component having a
grating, the grating comprising a plurality of curves bulged in the
direction in which the light beam from the light source is
propagated, the grating being symmetrical with respect to the
center line of the propagating light beam.
22. An optical disk head according to claim 21, wherein the
thickness and width of the light path are at least 100 times
greater than the wavelength of the light beam propagated through
the light path.
23. An optical disk head according to claim 21, further comprising
a position detecting optical means.
24. An optical disk head according to claim 21, wherein the light
path is disposed within the substrate.
25. An optical disk head according to claim 23, wherein the
position detecting optical means is an optical beam splitter.
26. An optical disk head according to claim 25, wherein the optical
beam splitter is a reflex diffractive optical component for
diffracting the light beam introduced by the light condensing means
into the light path and propagated therethrough so as to direct the
light beam sideways of the direction of propagation.
27. An optical disk head according to claim 21, wherein the light
condensing means is a reflective type, and posed on the bottom
surface of the substrate.
28. An optical disk head according to claim 27, wherein the optical
beam splitter, the light source, and the optical detector are
disposed on the bottom surface of the substrate.
29. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a light condensing means optically connected to the
light path so as to radiate the light beam propagated through the
light path upon an optical recording medium provided over a top
surface of the substrate and for guiding the light beam reflected
from the optical recording medium into the light path, an optical
detector for detecting the light beam propagated through the light
path guided by the light condensing means, and a position detecting
optical means comprising an optical beam splitter, the beam
splitter comprising a pair of curved gratings which are arranged
perpendicularly to the direction in which the light beam is
propagated, and are symmetrical to each other.
30. An optical disk head according to claim 29, further comprising
a reflex collimator disposed on the bottom surface of the
substrate, so as to collimate the light beam radiated from the
light source and propagated through the light path.
31. An optical disk head according to claim 30, wherein the
collimator is a reflex diffractive optical component and comprises
curved grating which includes a plurality of ellipses having major
axes in the direction in which the light beam is propagated,
wherein the canters of the elliptical curves are shifted one after
another progressively in the direction in which the light beam from
the light source are propagated.
32. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a light condensing means optically connected to the
light path so as to radiate the light beam propagated through the
light path upon an optical recording medium provided over a top
surface of the substrate and for guiding the light beam reflected
from the optical recording medium into the light path, an optical
detector for detecting the light beam propagated through the light
path guided by the light condensing means, and a position detecting
optical means comprising an optical beam splitter, the beam
splitter comprising a linear grating including a plurality of
linear lines.
33. An optical disk head according to claim 26, wherein the light
condensing means is a transmission type, and is disposed on the top
surface of the substrate so as to radiate the light beam
perpendicularly to the substrate.
34. An optical disk head according to claim 33, wherein the beam
splitter is disposed on the top surface of the substrate, and the
optical detector and the light source are disposed on the bottom
surface thereof.
35. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a light condensing means optically connected to the
light path so as to radiate the light beam propagated through the
light path upon an optical recording medium provided over a top
surface of the substrate and for guiding the light beam reflected
from the optical recording medium into the light path, an optical
detector for detecting the light beam propagated through the light
path guided by the light condensing means, and a position detecting
optical means comprising an optical beam splitter, the optical beam
splitter being a reflex diffractive optical component for
diffracting the light beam introduced by the light condensing means
into the light path and propagated therethrough so as to direct the
light beam sideways of the direction of propagation, the light
condensing means being a transmission type, and being disposed on
the top surface of the substrate so as to radiate the light beam
perpendicularly to the substrate, the beam splitter being disposed
on the top surface of the substrate, and the optical detector and
the light source being disposed on the bottom surface thereof, the
beam splitter comprising a pair of curved gratings arranged
laterally with respect to the light beam, and symmetrical to each
other with respect to the light propagating direction.
36. An optical disk head according to claim 35, wherein the
substrate is provided with a reflex collimator for collimating the
light beam output from the light source and propagated through the
light path.
37. An optical disk head according to claim 36, wherein the
collimator is a diffractive optical component, and includes a
plurality of elliptical curves having major axes in the direction
in which the light beam is propagated, wherein the canters of the
elliptical curves are shifted one after another progressively in
the direction in which the light beam from the light source is
propagated.
38. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a light condensing means optically connected to the
light path so as to radiate the light beam propagated through the
light path upon an optical recording medium provided over a top
surface of the substrate and for guiding the light beam reflected
from the optical recording medium into the light path, an optical
detector for detecting the light beam propagated through the light
path guided by the light condensing means, and a position detecting
optical means comprising an optical beam splitter, the optical beam
splitter being a reflex diffractive optical component for
diffracting the light beam introduced by the light condensing means
into the light path and propagated therethrough so as to direct the
light beam sideways of the direction of propagation, the light
condensing means being a transmission type, and being disposed on
the top surface of the substrate so as to radiate the light beam
perpendicularly to the substrate, the beam splitter being disposed
on the top surface of the substrate, and the optical detector and
the light source being disposed on the bottom surface thereof, the
beam splitter comprising a linear grating including a plurality of
linear lines.
39. An optical disk head according to claim 38, wherein the
substrate is provided with a reflex collimator for collimating the
light beam from the light source and propagated through the light
path.
40. An optical disk head according to claim 39, wherein the
collimator is a diffractive type, and comprises a curved grating
which includes a plurality of elliptical curves having major axes
in the direction in which the light beam is propagated, wherein the
centers of the elliptical curves are shifted one after another
progressively in the direction in which the light beam from the
light source in propagated.
41. An optical disk head according to claim 26, wherein the light
condensing means is@a transmission type, and disposed on the top
surface f the substrate so as to radiate the light beam from the
light source obliquely to the substrate.
42. An optical disk head comprising a substrate, a light path for
allowing light beam to propagate in a zigzag form, having a
thickness and width of at least 10 times greater than the
wavelength, a light source optically connected to the light path so
as to allow an incident light from the light source to propagate
therethrough, a light condensing means optically connected to the
light path so as to radiate the light beam propagated through the
light path upon an optical recording medium provided over a top
surface of the substrate and for guiding the light beam reflected
from the optical recording medium into the light path, an optical
detector for detecting the light beam propagated through the light
path guided by the light condensing means, and a position detecting
optical means comprising an optical beam splitter, the optical beam
splitter being a reflex diffractive optical component for
diffracting the light beam introduced by the light condensing means
into the light path and propagated therethrough so as to direct the
light beam sideways of the direction of propagation, the light
condensing means being a transmission type, and being disposed on
the top surface of the substrate so as to radiate the light beam
from the light source obliquely to the substrate, the beam splitter
comprising a pair of curved gratings arranged laterally with
respect to the light beam, and are symmetrical to each other with
respect to the light propagating direction.
43. An optical disk head according to claim 42, wherein the beam
splitter, the optical detector, and the light source are disposed
on the top surface of the substrate.
44. An optical disk head according to claim 42, wherein the beam
splitter is disposed on the top surface of the substrate, and the
optical detector and the light source are disposed on the bottom
surface of the substrate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to an optical disk head used in an
optical recording apparatus, and a method for producing the same.
More particularly, the present invention relates to an optical disk
head which is thin and lightweight, and achieves easy mechanical
alignment of components, and a method for mass-producing such
optical disk heads.
2. Description of the Prior Art:
An optical recording apparatus includes an optical disk head so as
to read signals recorded in an optical recording medium such as
compact disks (CD), optical disks, and optical card memories. The
optical head is necessarily equipped with a servocontrol such as a
focus servo or a track servo.
There is a typical optical disk head known in the industry
illustrated in "Autofocus Hitec Technologies" (edited by M. Kohno,
published by Keiei System Kenkyusha) which will be described by
reference to FIG. 1:
A light source 1 radiates a laser beam 17 which is made parallel by
a collimator lens 18 and caused to pass through a beam splitter 19.
Then it is focused on an optical disk 7 by an objective lens 20.
The laser beam is reflected from the optical disk 7, and is made
parallel by the objective lens 20. After being reflected from a
boundary face 19' of the beam splitter 19, is introduced into a
focus-track error detector optics 21 which includes a convex lens
and a cylindrical lens. Thus, a reproducing signal, a focus-error
signal and a track-error signal are read.
The known optical disk head shown in FIG. 1 has disadvantages in
that the optical system becomes complex and the mechanical
alignment of optical components requires high precision. Thus, the
resulting optical head is likely to become large, heavy and
costly.
In order to solve these problems, efforts are being made to develop
optical integrated circuits including a substrate in which a
waveguide and various optical components are provided. However, a
difficulty arises from the fact that light beam is propagated
throughout the waveguide as a wave having a crest-type distribution
of light intensity, thereby requiring the light beam to be treated
under the theory of wave optics. This means that the efficiencies
at which a light beam is introduced into the waveguide and output
therefrom are likely to reduce, and the optical information
propagated through the waveguide is one-dimensional.
Japanese Laid-Open Patent Publications Nos. 2-301702, 2-301703 and
2-301704 disclose planar reflection optical devices. These devices
employ a transparent substrate with reflective lenses so that a
light beam is allowed to propagate in a zigzag form through the
substrate but they have no optical pickup means for catching a
light beam reflected from an optical recording medium. As a result,
these devices cannot be used for an optical disk head.
SUMMARY OF THE INVENTION
The optical disk head of the present invention, which overcomes the
above-discussed and numerous other disadvantages and deficiencies
of the prior art, comprises a substrate, a light path for allowing
light beam to propagate in a zigzag form, having a thickness and
width of at least 10 times greater than the wavelength, a light
source optically connected to the light path so as to allow an
incident light from the light source to propagate therethrough, a
first light condensing means optically connected to the light path
so as to radiate the light beam propagated through the light path
upon an optical recording medium provided over a top surface of the
substrate, a second light condensing means for guiding the light
beam reflected from the optical recording medium into the light
path, and an optical detector for detecting the light beam
propagated through the light path guided by the second light
condensing means.
In a preferred embodiment, the thickness and width of the light
path is not smaller then 100 times the wavelength of the light beam
propagated through the light path.
In a preferred embodiment, the optical disk head is additionally
provided with a position detecting optical means.
In a preferred embodiment, the light path is disposed within the
substrate.
In a preferred embodiment, the first light condensing means is a
diffractive optical component having a curved grating which
comprises a plurality of curves which are bulged in the direction
in which the light beam from the light source are propagated and
symmetrical with respect to the center line of the propagating
light beam.
In a preferred embodiment, the second light condensing means is a
diffractive optical component having a grating which comprises a
plurality of curves which are bulged in the opposite direction to
the direction in which the light beam introduced into the light
path by the second light condensing means are propagated and
symmetrical with respect to the center line of the propagating
light beam.
In a preferred embodiment, the position detecting optical means is
an optical beam splitter.
In a preferred embodiment, the optical beam splitter is a reflex
diffractive optical component disposed on the top surface of the
substrate so as to face the optical recording medium, and has a
pair of lenses, the pattern of each grating comprising a group of
ellipses having equal eccentric ratios and major axes in the
direction in which the light beam is propagated, wherein the
centers of the ellipses are shifted one after another progressively
in the opposite direction to the direction in which the light beam
is propagated and the grating period diminishing toward the outside
peripheries.
In a preferred embodiment, the optical beam splitter comprises a
pair of reflex micro-Fresnel lenses disposed on the top surface of
the substrate.
In a preferred embodiment, the light path comprises a collimator
for collimating the light beam propagated through the light path
from the light source.
In a preferred embodiment, the collimator is a reflex diffractive
optical component.
In a preferred embodiment, the collimator comprises gratings which
include a plurality of ellipses having major axes in the direction
in which the light beam is propagated, wherein the centers of the
curves are shifted one after another progressively in the direction
in which the light beam is propagated.
In a preferred embodiment, the collimator is a micro-Fresnel
lens.
In a preferred embodiment, the first and second light condensing
means are transmission off-axis lenses disposed on the top surface
of the substrate so as to face the optical recording medium, and
wherein the beam splitter and the collimator are disposed on the
top surface of the substrate.
In a preferred embodiment, the light source and the optical
detector are disposed on the top surface of the substrate so as to
face the optical recording medium.
In a preferred embodiment, the light source and the optical
detector are disposed on the bottom surface of the substrate.
In a preferred embodiment, the light source and the collimator are
disposed in correspondence to each other with the substrate being
interposed, and wherein the optical detector and the optical beam
splitter are disposed in correspondence to each other with the
substrate being interposed.
In a preferred embodiment, the first and second light condensing
means are reflex off-axis lenses, and disposed on the bottom
surface of the substrate.
In a preferred embodiment, the second light condensing means is a
transmission diffractive beam splitter, and disposed on the too
surface of the substrate, and the split light beam is detected by
the optical detector.
In a preferred embodiment, the second light condensing means
comprises a pair of gratings which includes a plurality of curves
bulged in the opposite direction to the direction in which the
light beam introduced by the second light condensing means into the
light path are propagated therethrough, the curves being
symmetrical with respect to the center line of the propagating
light beam.
In a preferred embodiment, the light source and the optical
detector are disposed on the top surface of the substrate.
In a preferred embodiment, a light path for allowing light beam to
propagate in a zigzag form, having a thickness and width of at
least 10 times greater than the wavelength, a light source
optically connected to the light path so as to allow an incident
light from the light source to propagate therethrough, a light
condensing means optically connected to the light path so as to
radiate the light beam propagated through the light path upon an
optical recording medium provided over a top surface of the
substrate and for guiding the light beam reflected from the optical
recording medium into the light path, and an optical detector for
detecting the light beam propagated through the light path guided
by the light condensing means.
In a prferred embodiment, the thickness and width of the light path
are at least 100 times greater than the wavelength of the light
beam propagated through the light path.
In a preferred embodiment, the optical disk head is additionally
provided with a position detecting optical means.
In a preferred embodiment, the light path is disposed within the
substrate.
In a preferred embodiment, the light condensing means is a
diffractive optical component having a grating which comprises a
plurality of curves which are bulged in the opposite direction to
the direction in which the light beam from the light source are
propagated and symmetrical with respect to the center line of the
propagating light beam.
In a preferred embodiment, the position detecting optical means is
an optical beam splitter.
In a preferred embodiment, the optical beam splitter is a reflex
diffractive optical component for diffracting the light beam
introduced by the light condensing means into the light path and
propagated therethrough so as to direct the light beam sideways of
the direction of propagation.
In a preferred embodiment, the light condensing means is a
reflective type, and disposed on the bottom surface of the
substrate.
In a preferred embodiment, the optical beam splitter, the light
source, and the optical detector are disposed on the bottom surface
of the substrate.
In a preferred embodiment, the beam splitter comprises a pair of
curved gratings which are arranged perpendicularly to the direction
in which the light beam is propagated, and are symmetrical to each
other.
In a preferred embodiment, the optical disk head is additionally
provided with a reflex collimator disposed on the bottom surface of
the substrate, so as to collimate the light beam radiated from the
light source and propagated through the light path.
In a preferred embodiment, the collimator is a reflex diffractive
optical component and comprises curved grating which includes a
plurality of ellipses having major axes in the direction in which
the light beam is propagated, wherein the centers of the elliptical
curves are shifted one after another progressively in the direction
in which the light beam from the light source are propagated.
In a preferred embodiment, the beam splitter comprises a linear
grating including a plurality of linear lines.
In a preferred embodiment, the light condensing means is a
transmission type, and is disposed on the top surface of the
substrate so as to radiate the light beam perpendicularly to the
substrate.
In a preferred embodiment, the beam splitter is disposed on the top
surface of the substrate, and the optical detector and the light
source are disposed on the bottom surface thereof.
In a preferred embodiment, the beam splitter comprises a pair of
curved gratings arranged on opposite sides of the direction in
which the light beam is propagated through the light path, and are
symmetrical to each other with respect to the light propagating
direction.
In a preferred embodiment, the substrate is provided with a reflex
collimator for collimating the light beam output from the light
source and propagated through the light path.
In a preferred embodiment, the collimator is a diffractive optical
component, and includes a plurality of elliptical curves having
major axes in the direction in which the light beam is propagated,
wherein the centers of the elliptical curves are shifted one after
another progressively in the direction in which the light beam from
the light source is propagated.
In a preferred embodiment, the beam splitter comprises a linear
grating including a plurality of linear lines.
In a preferred embodiment, the substrate is provided with a reflex
collimator for collimating the light beam from the light source and
propagated through the light path.
In a preferred embodiment, the collimator is a diffractive type,
and comprises a curved grating which includes a plurality of
elliptical curves having major axes in the direction in which the
light beam is propagated, wherein the centers of the elliptical
curves are shifted one after another progressively in the direction
in which the light beam from the light source is propagated.
In a preferred embodiment, the light condensing means is a
transmission type, and disposed on the top surface of the substrate
so as to radiate the light beam from the light source obliquely to
the substrate.
In a preferred embodiment, the beam splitter comprises a pair of
curved gratings arranged on opposite sides of the direction in
which the light beam is propagated through the light path, and are
symmetrical to each other with respect to the light propagating
direction.
In a preferred embodiment, the beam splitter, the optical detector,
and the light source are disposed on the top surface of the
substrate.
In a preferred embodiment, the beam splitter is disposed on the top
surface of the substrate, and the optical detector and the light
source are disposed on the bottom surface of the substrate.
According to another aspect of the present invention, there is a
method for fabricating an optical disk head, the method comprising
the steps of preparing a substrate including a light path,
preparing a single mold for molding diffractive optical components
used as a light condensing means and ia position detecting optical
means, and mounting the two diffractive optical components at one
time on the substrate.
Thus, the invention described herein makes possible the objective
of providing a small and lightweight optical disk head capable of
easy alignment of components.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention may be better understood and its numerous objects
and advantages will become apparent to those skilled in the art by
reference to the accompanying drawings as follows:
FIG. 1 is a diagrammatic view showing a prior art optical head;
FIG. 2 is a cross-sectional view showing a structure of an optical
head according to the present invention, particularly to show the
propagation and focusing of light beam;
FIG. 3 is a plan view showing the arrangement shown in FIG. 2;
FIG. 4 in a cross-sectional view showing a structure of a second
example of the optical head according to the present invention,
particularly to show the propagation and focusing of light
beam;
FIG. 5 is a cross-sectional view showing a structure of a third
example of the optical head according to the present invention,
particularly to show the propagation and focusing of light
beam;
FIG. 6 is a plan view showing the arrangement of FIG. 5;
FIG. 7 is a cross-sectional view showing a structure of a fourth
example of the optical head according to the present invention,
particularly to show the propagation and focusing of light
beam;
FIG. 8 is a plan view showing the arrangement of FIG. 7;
FIG. 9 is a cross-sectional view showing a structure of a fifth
example of the optical head according to the present invention,
particularly to show the propagation and focusing of light
beam;
FIG. 10 is a cross-sectional view showing a structure of a sixth
example of the optical head according to the present invention,
particularly to show the propagation and focusing of light
beam;
FIG. 11 is a plan view showing the arrangement of FIG. 10;
FIG. 12 is a cross-sectional view showing a structure of a seventh
example of the optical head according to the present invention,
particularly to show the propagation and focusing of light
beam;
FIG. 13 is a cross-sectional view showing a structure of an eighth
example of the optical head according to the present invention,
particularly to show the propagation and focusing of light
beam;
FIG. 14 is a plan view showing the arrangement of FIG. 13;
FIG. 15 is a cross-sectional view showing a structure of a ninth
example version of the optical head according to the present
invention, particularly to show the propagation and focusing of
light beam;
FIG. 16 is a cross-sectional view showing a structure of a tenth
example of the optical head according to the present invention,
particularly to show the propagation and focusing of light
beam;
FIG. 17 is a plan view showing the arrangement of FIG. 16;
FIG. 18 is a cross-sectional view showing a structure of an
eleventh example of the optical head according to the present
invention, particularly to show the propagation and focusing of
light beam;
FIG. 19 is a plan view showing the arrangement of FIG. 18;
FIG. 20 is a cross-sectional view showing a structure of a twelfth
example of the optical head according to the present invention,
particularly to show the propagation and focusing of light beam;
and
FIG. 21 is a cross-sectional view showing a structure of a
thirteenth example of the optical head according to the present
invention, particularly to show the propagation and focusing of
light beam.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
EXAMPLE 1
Referring to FIGS. 2 and 3, a light beam radiated from a light
source 1 bounce within a substrate 2. An optical disk 7 is placed
above the substrate 2. The surface of the substrate 2 that is
opposite to the optical disk 7 is called "the top surface", whereas
the opposite side of the top surface is called "bottom surface".
More specifically, the light beam is reflected from the bottom
surface of the substrate 2 so that they are propagated along zigzag
paths 13. The substrate 2 is made of a glass plate having a
thickness (in the direction of z) of 3 mm, a width (in the
direction of x) of 10 mm, and a length (in the direction of y) of
25 mm. Any material can be used for the substrate 2 if it allows
light waves to pass through. Glass plate such as quartz glass is
desirable because of its resistance to heat. The substrate 2 is
covered with a reflection layer 11a which can be a metal layer such
as Al and Au or alternatively a dielectric layer.
The light source 1 such as a semiconductor laser element is mounted
on one side of the substrate 2 so as to radiates laser beam having
a wavelength of 0.78 .mu.m. The laser beam is propagated through
the zigzag path 13 in such a manner that the optical axis is
inclined at 30.degree. to the z axis. On the top surface of the
substrate 2 are provided a reflex-type diffractive collimator lens
3 (hereinafter referred to as "collimator"), transmission condenser
lenses 4a, 4b and a pair of reflex-type diffractive beam splitters
5 having a pair of lenses 5a and 5b in this order.
The laser beam propagated along the zigzag path 13 is reflected
from the reflection layer 11a and are introduced into the
collimator 3, made of a lens having a focal length of 6.9 mm and a
diameter of 3 mm. The collimator 3 maintains the angle .theta., for
example, 30.degree. at which the laser beam is propagated, and
collimates the laser beam. The collimated light beam with a width
of 2.5 mm is propagated along the zigzag path 13, and is output by
a transmission condenser lens 4a having a diameter of 3 mm and a
focal length of 3 mm from the substrate 2 toward the optical disk 7
with an angle .theta..sub.1.
The laser beam 9 is focused on the optical disk 7 and reflected
therefrom. The reflected laser beam 10 is introduced into a second
transmission condenser lens 4b having a focal length of 3 mm and a
diameter of 3 mm. The input laser beam 10 is collimated and
propagated as propagating light beam 8' along the zigzag path 13 at
a predetermined angle. In this way the propagating light beam 8' is
introduced into the reflex-type diffractive beam splitter 5 having
a pair of lenses 5a and 5b which are covered with a reflection
layer 11b. The lenses 5a and 5b have lengths of 3 mm in the
directions of y and x, and a focal length of 6.9 mm. The incident
light beam to the lenses 5a and 5b are split into two beam, and
after being reflected from the bottom surface of the substrate 2,
they are introduced into an optical detector 6. The optical
detector 6 includes four detecting sections 6a to 6d arranged
perpendicular to the direction of propagation so that each light
intensity measured by each detector is utilized as a reproducing
signal, a focusing error signal and a track-error signal.
The collimator 3 and the diffractive beam splitter 5 can be made of
an in-line type reflex diffracting optical lens having a curved
grating whose maximum depth or thickness is 0.28 .mu.m. The
transmission condenser lenses 4a and 4b can be made of off-axis
diffractive lenses each having a curved grating whose maximum depth
is 1.3 .mu.m. Both collimator 3 and the condenser lenses 4a, 4b
focus the light beam by utilizing the optical diffraction. The
in-line type diffractive optical lens in a lens which ensures that
the angle of the optical axis of an incident light is in agreement
with that of the output light. The off-axis diffractive lenses
ensure that the angle of the optical axis of an incident light is
not in agreement with that of the output light. In general,
diffraction lenses are a few .mu.m thin at most, and it is possible
to integrate these lenses on the surface of the substrate 2,
thereby facilitating the alignment of these lenses. Accordingly, a
lightweight, stabilized optical disk head can be achieved.
In this example, the curved gratings in the collimator 3 and the
lenses 5a and 5b in the diffractive beam splitter 5 are formed with
multiple elliptical curves within the zigzag path 13 wherein the
elliptical curves have major axes in the direction of y with the
same eccentric ratio. Each curve has diminishing grating period
toward the periphery. The centers of the elliptical gratings are
shifted toward the input or output sides (in a lens 3 toward the
output side, that is, in the direction of y and in a lens 5 or
diffractive beam splitter toward the input side, that is, the
direction of -y). The curved gratings are advantageous in that
neither coma nor astigmatism occur, thereby facilitating the
collimation and focusing.
The collimator 3, that is, the in-line type reflex diffractive
collimator which will be described in greater detail:
In order to constitute the lens 5a or 5b, the phase shift .PHI.,
when it is in the coordinate system of which is the origin is the
lens center, is expressed by: ##EQU1## where f is the focal length,
.lambda. is the wavelength of the light source, n' is the
refractive index and .theta. is the angle of propagation, wherein
k=2.pi./.lambda. and m is an integer which satisfies
0.ltoreq..PHI..ltoreq.2.pi..
If the maximum thickness of the lens or the maximum depth of the
groove is L.sub.max, the value .PHI. corresponds to the
distribution of L thickness of the lens, which is expressed as
follows:
If .PHI. is zero, it will be inferred what pattern the grating will
take with no thickness, and the grating pattern can be inferred to
be an ellipse which has a center at the position (0,
m.lambda.tan.theta./n'cos.theta.), with the lengths of the major
axis and the minor axis expressed as follows:
The length of the major axis: ##EQU2##
The length of the minor axis: ##EQU3##
Thus, the ratio of the major axis to minor axis=1/cos.theta.
It will be understood that the ratio of the major axis to the minor
axis and the shift of the center of the ellipse increase with an
increase in the incident angle .theta.. This phenomenon can be
verified by analysis based on the ray approximation theory.
Off-axis transmission diffractive lenses used as transmission
condenser lenses 4a and 4b have a plurality of curves of arched
pattern or parabola arranged in the direction in which the light
beam is propagated. Each curved grating is bulged in the opposite
direction to the input or output sides. The output condenser lens
4a has grooves of an arched shape bulged in the direction in which
light beam is propagated (in the y direction), and its grating
period diminishes progressively in the light propagating direction.
The input condenser lens 4b has grooves of an arched shape bulged
in the opposite direction to the direction in which the light beam
is propagated, and its grating period increases progressively in
the direction in which the light beam is propagated. The curved
gratings of the condenser lenses 4a and 4b are symmetrical with
respect to the center line of the light beam.
The output off-axis condenser lens 4a will be described in greater
detail:
When the focal length is f.sub.1, the wavelength of laser beam from
the light source 1 is .lambda., the index of refraction of the
light path is n', the angle of propagation is .theta., the angle of
projection from the lens 4a is .theta..sub.1, the phase shift
.theta..sub.1 is expressed as follows: ##EQU4## wherein m is an
integer which satisfies 0.ltoreq..PHI..sub.1 .ltoreq.2.pi..
It will be understood from this equation that the pattern of the
grating having no thickness has a center at the position expressed
by:
Herein, if the length of the major axis is 2a, the grating will
become an elliptical pattern with a minor axis 2b which is
2a.sqroot.1-n'.sup.2 sin.theta.. The ratio of the major axis to the
minor axis is 1/.sqroot.1-n'.sup.2 sin.sup.2 .theta., wherein a is
expressed by the following equation: ##EQU5##
The center of the ellipse is spaced from the region of the lens 4a
in the direction of -y, and the grating of the lens 4a becomes an
arched curve in the end portion of the major axis of the elliptical
curve. This is verified by analysis based on the ray approximation
theory.
Preferably, the collimator 3, the condenser lenses 4a and 4b, and
the beam splitter 5a and 5b have saw-tooth cross-sections so that
they enable the light beam to reflect from or to pass through
highly efficiently. Patterns of these optical components can be
made on an extra substrate. An electron beam resist such as PMMA or
CMS with an appropriate thickness is coated on the substrate. Then,
an electron beam is radiated on the resist controlling the electron
beam dose. A mold is fabricated from this pattern by a nickel
electrotyping or any other suitable method. By using the mold, the
lenses 3, 4a, 4b and 5 are formed on the substrate 2 using the
UV-setting resin or the like. This method ensures that these
components are in exact alignment, and that they have the same
characteristics. The diffractive lenses 3 and 5 are covered with
the reflection layers 11c and 11b such as Ag, Al or Au.
In addition, the reflection layers 11b and 11c are covered with a
protective layer from a thickness of 1000 angstroms to a few .mu.m,
which includes metal layers such as Cu or Cr, synthetic resin
layers such as UV hard resin, paint such as lacquer, dielectric
multi-layers or any other protective layers such as SiO, SiO.sub.2,
MgF.sub.2, SiC, graphite, diamond. The protective layers protect
the reflection layer from being damaged or scratched and from being
oxidized. The protective layer is of particular advantage when an
Ag layer is used because silver is liable to oxidizing.
The signals recorded in the optical disk are reproduced in
accordance with the sum of light intensities measured by the
detecting sections 6a, 6b, 6c, and 6d in the optical detector
6.
The optical detector 6 also monitors a focus-error signal and a
track error signal. A focus-error signal is detected by a known
method. As shown in FIG. 3, the pairs of detecting sections 6a and
6b and 6c and 6d are arranged so that light beams split by the beam
splitter 5 are focused at the center between each pair of detecting
sections. The focus error signal is obtained from the difference
between the outputs from the detecting sections 6a and 6b (6a-6b)
or the difference between the outputs from the detecting sections
6d and 6c (6d-6c). When the optical disk 7 is exactly positioned at
the point of focus, the focus-error signal becomes zero. When the
optical disk 7 moves in the -z direction away from the substrate 2,
the propagating light beam 8' becomes a converging spherical wave,
thereby causing the split two light beams to approach each other.
Thus the focus error signal becomes minus. In contrast, when the
optical disk 7 moves from the point of focus along the z axis near
to the substrate 2, the propagating light beam become a diverging
spherical wave, and the split propagating light beams move apart
from each other. Thus, the focus-error signal becomes plus. By
using this focus-error signal, the focusing is controlled.
A track-error signal is detected by the difference in light
intensity between the propagating light beams split by a known
push-and-pull method. More specifically, the track-error signal is
detected by subtracting the sum of the outputs of the detecting
sections 6c and 6d from the sum of the other detecting sections 6a
and 6b (6a+6b-6c-6d). When the track error signal is zero, an exact
tracking is achieved, and when the track error signal is other than
zero, it indicates that an out-of-track occurs. Adjustment is
needed. In this way the detection of a track-error signal enables
the control of tracking.
The controls of focusing and tracking are performed by moving the
substrate 2 as a whole by an actuator to an optimum position on the
basis of the error signals detected.
The length of the zigzag path 13 depends upon the sizes of the
collimator 3, the condenser lenses 4 and the beam splitter 5 (in
the order of a few mm). The width and thickness are also In the
order of a few mm. Thus, the path 13 can be formed in various
patterns such as in a zigzag form so that light beam can be
propagated not as wave but as ray. This is a solution to the
problems of the known optical devices having optical waveguide
which must be handled in accordance with the wave optics theory. In
the present invention, when the thickness and width of the light
path 13 are ten times greater than the wavelength, the light beam
is propagated through the path 13 as rays rather than as waves. If
they are 100 times greater than the wavelength, the light beam is
propagated as a perfect ray. The present invention requires that
the light path 13 is at least 10 times thicker then the wavelength
of light, preferably 100 times thicker.
EXAMPLE 2
Referring to FIG. 4, this example is different from Example 1 in
that the light source 1 and the optical detector 6 are mounted on
the opposite surface of the substrate 2 to the optical disk 7. This
arrangement is advantageous in that the optical detector 6 and the
light source 1 (a semiconductor laser generator) are not likely to
come into contact with the optical disk 7. Thus, a relatively free
layout is possible for positioning these components. In addition,
since the light source 1 and the optical detector 6 can be located
near an electric control circuit, the electric wiring is
simplified.
EXAMPLE 3
Referring to FIGS. 5 and 6, this example is different from Example
2 in that the collimator 3' and the beam splitter 5' are made of
off-axis diffractive lenses so that the optical axes of the light
beam generated from the light source 1 and the light beam incident
to the optical detector 6 are vertical to the substrate 2 (in the z
direction), and the light source 1 and the optical detector 6 are
positioned right below the lenses 3' and 5' on the substrate 2,
respectively. The other arrangement is the same as that in FIG. 4.
Since the optical axes of the light beam emitted from the light
source 1 and the light beam incident to the optical detector 6 are
vertical to the substrate 2, the output surface of the light source
1 and the surface of the optical detector 6 are allowed to be
parallel to the substrate 2. This facilitates the mounting of the
optical detector 6 and the light source 1 on the substrate 2. It is
effective to use either the off-axis collimator lens 3' or the
off-axis beam splitter so as to make the output surface of the
light source 1 vertical to the substrate 2.
The grating patterns of the off-axis reflective lens 3' and 5' are
similar to that of the transmission condenser lens 4. The grating
of the lenses 3' and 5' consist of multiple curves which are bulged
or parabolic in opposite directions to the input side or the output
side of substantially parallel light beam, and the grating period
of the collimator 3' becomes gradually large in the direction in
which the light beam Is propagated. The curves of each grating are
symmetrical to the central axis extending in the direction of
propagation. The gratings 5a' and 5b' of the beam splitter 5 have
grating periods which diminish in the direction of propagation (in
the y direction).
The off-axis collimator 3' will be described:
When the focal length is f.sub.2, and the wavelength of the light
source 1 is .lambda., the index of refraction of the zigzag path 13
is n', and the angle of propagation is .theta., the phase shift
.PHI..sub.2 in the coordinates system of which the origin is the
lens center will be expressed by: ##EQU6## wherein m is an integer
which satisfies 0.ltoreq..PHI..sub.2 .ltoreq.2.pi..
It will be understood from this equation that the pattern of the
grating having no thickness has a center at the position expressed
by: ##EQU7##
The ratio of the major axis to the minor axis is 1/cos.theta.. The
center of the ellipse is separated in the y direction from the
position of the lens 3'; therefore, the grating pattern of the lens
3' becomes bulged or arched which is symmetrical with respect to
the major axis in the neighborhood of end portions of the major
axis. This phenomenon is verified by analysis based on the ray
approximation theory.
By combining the lenses 3' and 5' of an off-axis type, changes in
the angle of diffraction due to variations in the wavelengths of
the light source 1 can be mutually negated, thereby preventing the
deterioration of optical characteristics.
EXAMPLE 4
Referring to FIGS. 7 and 8, the light source 1, the diffracting
grating condenser lens 4', a condenser lens 12 as a beam splitter,
and the optical detector 6 are mounted on the top surface of the
substrate 2 in the direction of propagation. The bottom surface of
the substrate 2 is covered with a reflection layer. The grating
condenser lens 4', having a similar grating pattern to that of the
diffractive condenser lens 4a in Example 1, also functions as a
collimator 3. The condenser lens 12 has the gratings 12a and 12b
with almost the same pattern as those of the gratings 5a' and
5b'.
The light beam generated from the light source 1 is reflected from
the bottom of the substrate 2, and passed through the condenser
lens 4' and are focused on the optical disk 7. The light beam
reflected from the optical disk 7 is split by the gratings 12a and
12b, and entered into the zigzag path 13. The propagating light
beam 8' in the zigzag path 13 is led into the optical detector 6
having detecting sections 6a to 6d.
In this example, the condenser lens 4' functions as a collimator,
and the condenser lens 12 functions as a beam splitter. Thus, the
number of components can be reduced, thereby resulting in a compact
size and avoiding the lose of light.
EXAMPLE 5
Referring to FIG. 9, the optical components are disposed on the
bottom surface of the substrate 2. Instead of the transmission
condenser lenses 4a and 4b in Example 1, reflex condenser lenses
14a and 14b are employed. The other optical components are the same
as those used in Example 1, except for the provision of them on the
bottom surface. The bottom surface of the substrate 2 is covered
with a reflection layer 11a excluding an area near the light source
1 and the optical detector 6. The top surface of the substrate 2 is
covered with reflection layers 11c and 11b excluding an area
through which the light beam reflected from the condenser lens 14a
is output toward the optical disk 7 and returned toward the
condenser lens 14b.
When a reflection lens is used for a condenser lens, the optical
characteristics are enhanced if the numerical aperture is
relatively large, for example, 0.45. When a reflex lens is used for
a diffractive lens, the thickness of the grating can be reduced by
1/5 compared with when a transmission lens is used. This
facilitates the electron-beam drawing method, and enhances the fine
patterning. However, the reflex condenser lenses 14a and 14b must
be provided on the bottom surface of the substrate 2, thereby
prolonging the focal length by the thickness of the substrate 2. If
the numerical aperture of the lens is to be identical to that of
the condenser lens 4, it is required to enlarge the diameter of the
lens.
EXAMPLE 6
Referring to FIGS. 10 and 11, all the optical components are
disposed on the bottom surface of the substrate 2. A reflex grating
collimator 3, a reflex grating beam splitter 15 having a curved
grating, and a reflex grating condenser lens 14 are disposed at
intervals in the direction in which light beam is propagated. On
each side of the reflex diffractive collimator 3 are disposed pairs
of detecting sections 6a and 6b, and 6c and 6d.
The bottom surface of the substrate 2 is covered with a reflection
layer 11a which covers the neighborhood of the collimator 3 up to
the neighborhood of the reflex diffractive condenser lens 14. The
top surface of the substrate 2 is covered with a reflection layer
11b excluding an area opposite to the condenser lens 14.
The diffractive condenser lens 14 has a plurality of curves bulged
in the opposite direction to the direction in which the light beam
from the light source 1 is propagated, wherein the curves are
symmetrical with respect to the central axis extending in the
direction of propagation.
The light beam emitted from the light source 1 is reflected from
the reflection layer 11b on the top surface of the substrate 2 and
collimated by the collimator 3. The light beam reflected from the
collimator 3 reach the reflex condenser lens 14 and reflect
therefrom. Then, the light beam is let to the optical disk 7 which
is projected perpendicularly to the substrate 2, and reflect from
the condenser lens 14. The reflected light beam is propagated
through the zigzag path 13 in the direction of -y. This light beam
is split by the beam splitter 15 and passed through the pairs of
detecting sections 6a and 6b, and 6c and 6d, respectively.
The beam splitter 15 includes a pair of lenses 15a and 15b, which
are inclined in the grating direction so as to split the light beam
propagated through the zigzag path 13 sideways with respect to the
direction of propagation (the direction of -y). The cross-sections
of the curved gratings are rectangular.
As is evident from the foregoing examples, the light beam emitted
from the light source 1 and that reflected from the optical disk 7
are propagated in opposite directions through the zigzag path 13.
The folded track system reduces the size of the optical disk head.
Because of the rectangular cross-section of the beam splitter 15,
the efficiency of diffraction becomes about 40% to 50%, and as a
whole the loss of light beam is minimized.
EXAMPLE 7
Referring to FIG. 12, the light source 1 is disposed on the bottom
surface of the substrate 2, and the reflex collimator 3, the reflex
beam splitter 15, and the off-axis transmission condenser lens 4'
are disposed on the top surface of the substrate 2 in the direction
in which light beam is propagated. The light beam emitted from the
light source 1 and propagated through the zigzag path 13 is
projected perpendicularly to the substrate 2 through the
transmission lens 4' and reach the optical disk 7. They reflect
from the optical disk 7 and are introduced into the zigzag path 13
through the condenser lens 4'. The other structure is the same as
that of Example 6.
In this example, the light beam is obliquely projected onto the
transmission condenser lens 4', and output therefrom
perpendicularly to the substrate 2.
EXAMPLE 8
Referring to FIGS. 13 and 14, instead of using the reflex
collimator 3 and the reflex beam splitter 15 having a curved
grating, a reflex beam splitter 16 having a linear grating is
employed. The linear grating includes a plurality of lines in
parallel with the direction in which the light beam is propagated.
A pair of detecting sections 6a and 6b are located on one side of
the light source 1, and another pair of detecting sections 6c and
6d are located on the other side thereof. The other structure is
the same as that of Example 6.
EXAMPLE 9
Referring to FIG. 15, the light source 1 is disposed on the bottom
surface of the substrate 2, and a reflex beam splitter 16 having a
linear grating is disposed on the top surface of the substrate 2.
The bottom surface of the substrate 2 is covered with a reflection
layer 11a from which the light beam is reflected and led to an
off-axis transmission condenser lens 4' which is disposed on the
top surface of the substrate 2. The light beam is projected
perpendicularly to the substrate 2 from the transmission condenser
lens 4' and reflected therefrom. The reflected light beam is led
into the zigzag path 13, and split into two parts which irradiate
the respective pairs of detecting sections 6a and 6b, and 6c and
6d.
This example is advantageous in that the optical disk head is
reduced in size, and simplified in structure.
EXAMPLE 10
Referring to FIGS. 16 and 17, the light source 1 is positioned
right below the off-axis reflex collimator 3'. Adjacent to the
collimator 3' is disposed the reflex beam splitter 16. This example
is different from Example 9 in that the light source 1 emits a
laser beam perpendicularly to the substrate 2. The pairs of
detecting sections 6a and 6b, and 6c and 6d are linearly disposed
at right angle to the light source 1 and the direction in which the
light beam is propagated. The other structure Is the same as that
of Example 9.
The optical disk head of this example is advantageous in that the
detecting sections 6a and 6b, and 6c and 6d can be easily aligned
because of their positions at right angles to the light source 1.
In addition, since the reflective collimator 3' and the
transmission condenser lens 4 are an off-axis type, changes in the
diffractive angle due to changes in wavelength can be mutually
cancelled, thereby preventing the deterioration of optical
characteristics.
EXAMPLE 11
Referring to FIGS. 18 and 19, the transmission condenser lens 4 has
an angle of exit of 3.degree. or so with respect to the substrate
2, and the light source 1 is disposed on the top surface of the
substrate 2. The light beam which is projected upon the optical
disk 7 and reflected therefrom are introduced into the zigzag path
13 through the transmission condenser lens 4. The light beam follow
a different path 8' (indicated by the dotted lines) from the path 8
(indicated by the solid line) and are propagated through the zigzag
path 13 in the -y direction. The reflex beam splitter 5' is located
at a position where the light beam emitted from the light source 1
are not allowed to enter but the light beam reflected from the
optical disk 7 are allowed to enter. The advantage of this example
is that the optical disk head can be reduced in size, and the loss
of light is minimized. In addition, the crosstalk within the zigzag
path 13 is reduced, thereby increasing the SN ratio.
EXAMPLE 12
Referring to FIG. 20, the light source 1 and the optical detector 6
are disposed on the bottom surface of the substrate 2 unlike
Example 11. The provision of them on the bottom surface of the
substrate 2 prevents them from coming into contact with the optical
disk 7, thereby securing a space around the substrate 2. The small
intervals among the light source 1, the optical detector 6, and the
electric control circuit facilitate the electric wiring.
EXAMPLE 13
Referring to FIG. 21, instead of the reflex collimator of Example 1
a reflex micro-Fresnel lens 3" is used, and instead of the reflex
beam splitter, a beam splitter 5" including a pair of reflex
micro-Fresnel lens 5a" and 5b" are used. The other structure is the
same as that of Example 1. The micro-Fresnel lenses 3", 5a" and 5b"
include a plurality of concentric curved gratings, thereby
facilitating the fabrication of the optical disk 7.
Throughout the examples the light beam is propagated within the
zigzag path by covering the substrate with a reflex covering but it
is possible to provide the path on the substrate. When the angle of
propagation is larger than the critical angle proper to the path,
it is not required to provide the reflection layer.
The application of the present invention is not limited to an
optical disk system but it can be applied to other optical
recording apparatus using an optical recording medium.
It is understood that various other modifications will be apparent
to and can be readily made by those skilled in the art without
departing from the scope and spirit of this invention. Accordingly,
it is not intended that the scope of the claims appended hereto be
limited to the description as set forth herein, but rather that the
claims be construed as encompassing all the features of patentable
novelty that reside in the present invention, including all
features that would be treated as equivalents thereof by those
skilled in the art to which this invention pertains.
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